Sight height

[Gene Carrell]

I spent yesterday morning doing load development with a 50cal Fred Harrison rifle; eclectic and beautiful. I found that it absolutely wanted bore-size rb's and 0.018 pillow ticking patch greased with mink oil.  Using 70gr of 3Fg (seemed better than 2Fg) bench groups of 5/8" @ 25yds and  <1" @ 50 yds were common; however, the groups were  5" high at 50yds (3"  at 25yds).  Does anyone know how much higher the front sight needs to be to bring  it in at 50yds?

[Daryl]

There are rules of thumb and forulae to figure just what the heights need to be.  Distance betweent he sigths is necessary.  I merely use a  file at the range while shooting and 'that looks about right' testing works every time.

[Mike R]

Is your rear sight such that it can be filed down and renotched?  Generally I dislike really high front sights on aesthetics grounds--and fortunately imost of my rifles required reducing the front blade with a file.  I have filed down the rear on my .32 squirrel rifle, however [and then screwed up the notch job--be careful] and brought it down. Another compromise is to go to a 6 oclock hold [unless you already are]. 

[Daryl]

My rifles are zeroed at 25 yards and that puts them generally about zero to 1/2" high at 50yards. My sights aren't very high, but height deos help with heat waves at a and when shooting in the winter time.  The trouble with high sights, the factory rifles with adjustable sights for instance, is they give elevated flight to the ball, showing extremes as you are showing, GeneC, as in 2" difference between 25 and 50.  2" difference is a lot to compensate for on small targets. Note that most 'original' guns have low sights- there were a couple reasons - 1/. Less prone to damage when low to the barrel & 2/.- low trajectory making piont blank sighting possible on close targets, yet giving a longer range zero with the ball close to the line of sight.

[Gene Carrell]

Distance between sights is 25 1/2"  with front sight height 1/8" and rear 1/4". I can reduce rear 'some', but not much. I am already using a 6 o-clock hold. I was hoping someone had a formula to use as a guesstimation. I don't particularly care for too tall front sight either.  Shooting 2Fg powder dropped the group  at 25yds to the center of the target, but the best group was double the size of my best 3Fg group which shot higher. I need all the help I can get without handicaping with a larger benched group.

[ironwolf]

 Based on mathematical ratio, 70 thou.  is the change you need to make.
I derived this  like this:

    50 yds is 1800 inches
    Your 5" divided by 1800 is 0.0027777....  The correction factor/per inch
    Multiplied by your 25 1/2" is 0.0708313

  Isn't this fun?

  However for the reasons Daryl mentioned, don't take that much off your sight at once.  There are many factors other than sight relationship that affect point of impact.
  I normally only do that kind of math when building a new gun with untried sights, just to get on the paper.  All measurements are calculated from bore centerline.  And I always need to finish her off with the file at the range, just like Daryl said. but I'm much closer to start with.

  Have Fun, Kevin W

[Daryl]

I usuallly start sighting with  my sights dead even - then file a bit off the front to raise impact to the line of sight. 1/4" difference between them is a lot. Much depends on the load, of course, as higher velocity will flatten trajectory considerably, even though 100 yard velocity might not be much different.  Because the biggest influance in windage and trajectory takes place close in, a low initial velocity has more effect upo0n flattening the trajectory than one might expect.

[Gene Carrell]

Front is 1/8" (0.125) lower than rear. Thanks to all. I think that I will install a taller front and reduce the  height of rear as well to keep overall height of front down. Back to the range Monday morning. Yes, it is fun.

[T*O*F]

Front is 1/8" (0.125) lower than rear.

Gene,
You didn't give your barrel profile.  Measuring the height difference requires different math for swamped and tapered barrels, as opposed to a straight barrel.

[Gene Carrell]

It is a straight 15/16" bbl. OAL 40.5"

[ironwolf]

  That's why I use the bore centerline, but based on the target shot, it's still a 0.070 change.

  KW

[Herb]

Ironwolf nailed it.  For the math challenged, Brownell's catalog has a Front Sight Elevation Correction chart for distances between front and rear sights from 14" to 34", and errors of 1 through 6 inches at 100 yards.  You have to double the correction for 50 yard change.  This chart interpolates (between 25 and 26" sight radius) to a correction of .0708".  This chart may be on their web site.  You can look on Track of the Wolf's web site for a front sight of the correct height and dovetail width.  Or ask Fred Harrison which sight to use.

[Dphariss]

For a 36" sight radius the bullet will move 1" from each .01" added or taken away from the sight at 100 yards.
Formula.
Desired change on the target in inches times the sight radius in inches divided by the range in INCHES.

1*36/3600 will give .01"
1*30/1800 (50yards) will give .0167"

Dan

[ironwolf]

  No matter how you slice it,  for a 5" correction at 50 yds.,  with a sight rad. of 25 1/2",  you come up with 0.070833"

  KW

[Gene Carrell]

Thanks again to all. I will probably take 0.030" or so off the rear sight, then get the remainder from a replacement front that I already have. My old eyes need the wider blade of the replacement anyway.

[ironwolf]

  Sounds like a good plan, Gene.  And another good reason to burn more powder.

  K